Channel Assignment Based on Spatial Strategies in a Wireless Network Using Adaptive Antenna Arrays

ABSTRACT

Channels are assigned based on co-spatial constraints in wireless network using spatial division multiple access. In one example, the invention includes assigning a co-spatial constraint to each of a plurality of conventional traffic communications channels of a base station, and receiving a request from a user terminal to communicate using a traffic communication channel of the base station. The invention further includes measuring a quality parameter of the request deriving a co-spatial constraint for the user terminal, assigning the user terminal co-spatial constraint to the user terminal, and assigning the user terminal to a traffic communication channels having a channel co-spatial constraint that is no less than the user terminal co-spatial constraint and that has no more assigned radios than permitted by the channel co-spatial constraint.

The present application is a Continuation application claiming priorityfrom U.S. patent application Ser. No. 10/112,164, filed on Mar. 28,2002, entitled Channel Assignment Based on Spatial Strategies in aWireless Network Using Adaptive Antenna Arrays.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention applies to the field of wireless communicationssystems using adaptive antenna arrays and, in particular, to allocatingcommunications channels and terminals using spatial strategies in aspatial division multiplexed wireless communications system.

2. Description of the Prior Art

A typical wireless communications system is generally subdivided intocells. A cell is generally thought of as a distinct geographic area,although cells usually overlap in reality. A cell is generallyassociated with a base station providing service to user terminals thatenter the cell, i.e., the base station's service area. Thus, a cell mayalso be thought of as a collection of remote terminals communicatingwith a particular base station at a certain time. Thus, while cells arepictured geographically, it is possible for two user terminals in closeproximity to be in different cells, so long as they are communicatingwith different base stations of the wireless radio network.

Adaptive antenna arrays and SDMA (Spatial Division Multiple Access)enable a wireless system to use strategies to reduce interference andenhance system capacity. These strategies include 1) increasing thesignal to interference ratio on the uplink (user terminal to basestation) by adjusting received signal samples based on the location of aremote terminal and the RF environment, 2) concentrating signal power tothe intended user terminal (beam-forming), and 3) placing nulls to userterminals using similar or the same frequency resources, such asterminals using the same channel on the downlink (base station to userterminal), among others. With these strategies, adaptive arrays cangreatly enhance the capacity of a wireless system.

Using various SDMA strategies, as described above, a single base stationmay be able to communicate with more than one user terminal on the sameconventional communications channel. The number of user terminals withwhich a base station can successfully communicate using a singlecommunications channel varies. It can depend on the number of other userterminals on other channels, the nature of physical obstructions to theradio signals, the amount of RF (radio frequency) noise in theenvironment, and the design of particular radios and the overall systemamong other factors.

Prior art SDMA systems have generally used one conventional channel forone user terminal, and used the co-channel interference mitigatingcapabilities provided by SDMA for mitigating interference to co-channeluser terminals in other cells. A co-channel user terminal can be viewedas another user terminal using the same conventional channel. Forco-channel users communicating with another base station, in a differentcell, the reuse frequency of the channel determines how near theco-channel users are. This affects how much co-channel interference iscreated. SDMA used to increase reuse frequency can increase the capacityof the system by allowing more aggressive frequency reuse.

As an alternative, the SDMA system can assign a predetermined number ofuser terminals to each channel. For example, three user terminals usingSDMA could share each channel. Unfortunately, a system with apredetermined number of user terminals is unlikely to operate at maximumcapacity, or to provide optimum quality of service. The number ofco-spatial users that can successfully share a channel typically dependson the individual characteristics of each user terminal and itsreception on its assigned channel. In most real systems, some userterminals will be able to successfully share a channel with moreco-spatial users than others.

Therefore, using a predetermined number for co-spatial terminals willlikely result in some channels being overused and some being underused.Underused channels waste capacity, and overused channels may have anunacceptably low quality of service. In order to ensure high qualityservice on all channels, some channels will be underused. This reducesthe capacity benefits that an SDMA system can offer.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example, and not by wayof limitation, in the figures of the accompanying drawings in which likereference numerals refer to similar elements and in which:

FIG. 1 is a flow chart of a process for assigning a channel to a userterminal implemented in accordance with an embodiment of the invention;

FIG. 2 is a flow chart of a process for assigning a channel using staticchannels assignment in accordance with an embodiment of the presentinvention;

FIG. 3 is a diagram of a base station in communication with userterminals over two channels using co-spatial constraints;

FIG. 4 is a diagram of a base station in communication with userterminals over two channels using other spatial strategies;

FIG. 5 is a simplified block diagram of a base station on which anembodiment of the invention can be implemented;

FIG. 6 is a simplified block diagram of a remote terminal on which anembodiment of the invention can be implemented.

DETAILED DESCRIPTION OF THE INVENTION

A communications channel can be assigned to a user terminal by firstdetermining a spatial strategy, such as a co-spatial constraint for theuser terminal. Alternatively, user terminals can be assigned to acommunications channel by comparing a co-spatial constraint assigned tothe user terminal to those assigned to the available channels. Terminalswith similar constraints can be grouped on the same channel. Such anapproach can be used to optimize system capacity.

The capacity of a wireless communications network can be increased byallowing different radio communications channels to support differentnumbers of co-spatial users. The number of co-spatial terminals for eachconventional channel can be determined based on the capacity of eachterminal to be co-spatial with other terminals in the existing radiofrequency (RF) environment, among other things. Any of a number ofdifferent quality parameters, such as distance from the base station,can be determined for each terminal. A spatial strategy can then beformulated for each terminal based on the measured parameter. Terminalswith similar spatial strategies can be assigned to the same channel.

Assigning a Terminal to a Conventional Channel

Referring to FIG. 1, the base station detects the arrival of a new userterminal 102. This may occur when the base station receives a signalfrom the new terminal. This signal will generally be some form of accessrequest caused by a handoff or a new connection, such as a configurationrequest burst, a channel assignment request, or an answer to a page.Alternatively, the base station can already have a connection with thenew terminal, but changes in the RF environment, or other factors, mayindicate that a channel reassignment is helpful or otherwise desirable.

Using a received signal, the base station can determine a spatialstrategy for the new terminal 104. The spatial strategy can include aconstraint on co-spatial users, null-placing, beam-forming, variousdiversity transmission schemes, space-time coding, and other techniques.This may be done, for example, by measuring a quality of the receivedsignal or by receiving a quality measurement in the signal made by theremote 103. One such parameter is the signal strength of the receivedsignal. A spatial strategy, such as a co-spatial constraint, can then bedetermined from the measurement. Alternatively, the new terminal maymeasure the strength of a signal it receives from the base station. Thatsignal can be a standard signal broadcast to all terminals, such as abroadcast channel (BCCH) signal or a signal from a special measurementprotocol. The signal received from a new remote at the base station mayalready have the quality parameter included or it can be determinedlater. Various other measurements, such as the signal to noise ratio(SNR), the signal to interference ratio (SIR), the distance of thesecond radio from the first radio, the signal to interference and noiseratio (SINR), some quality of service (QoS) designation of the secondradio, some mobility designation (e.g., mobile/fixed or fast/slowterminal) of the second radio, the actual mobility of the second radio,the Doppler shift of the received signal, the Doppler spread of thereceived signal, the velocity of the second radio, the angle spread(statistics based on the angles of arrival) of the received signal, andnumerous other metrics and parameters known in the art may also be usedin determining the co-spatial constraint of the new terminal.

The co-spatial constraint or other spatial strategy can depend on themobility of the new terminal. If the new terminal is a mobile unittraveling at a fast rate, for example a cell phone in a car, the newterminal will likely be given more severe constraints on the number ofco-spatial terminals than stationary or slow-moving terminals. The basestation may measure the speed of the new terminal using a variety oftechniques, including triangulation or Doppler shift. Then, the basestation can calculate a co-spatial constraint for the new terminal basedon this measurement.

The co-spatial constraint or other spatial strategy can also bedetermined based on the distance of the new terminal from the basestation. If the new terminal is a mobile unit this distance can vary onarrival at the base station, and even during the connection. the basestation can measure the distance to the new terminal usingtriangulation, signal delay, or some other method. The base station canthen determine a co-spatial constraint for the new terminal based onthis measured parameter. Since the base station may use a lower powerlevel to communicate with nearby terminals than for communications withterminals relatively farther away, assigning these terminals co-spatialconstraints that tend to group them on the same channel can haveadditional benefits.

Spatial strategies can also be determined completely or partially usinginformation from the user terminal. The user terminal can listen to andmeasure existing traffic on the network and determine it own qualityparameters. It can even include a co-spatial constraint determination ina message sent to the base station. Alternatively, the new terminal mayuse a signal transmitted to the base station to inform the base stationof the new terminal's subscription level. For example, a user could payextra for a quality of service level that guarantees that it will sharea channel with no more than a maximum of two terminals. The signaltransmitted by the new terminal to the base station may also haveinformation about the capacity of the hardware of the terminal to handlespatial processing.

As with any other spatial strategy, the co-spatial constraint, i.e., thenumber of additional users with which the terminal can share a channelfor communications with the same base station, can be determined in avariety of ways using a variety of parameters and metrics. Any number ofparameters can be combined for the determinations. Some of theparameters may also overlap. For example, in a system using the distancemetric, the distance may be estimated using a signal strength metric.

Once a co-spatial constraint of the new terminal has been determined,the base station finds an appropriate channel 106 on which to exchangecommunications with the terminal. In one embodiment, the base stationfinds channels that are used for communications with user terminals withthe same co-spatial constraint as the new terminal. As an example,consider a determination that a new terminal seeking network access isable to share a channel with three other user terminals. This can becalled a co-spatial constraint of four. To add the new terminal, thebase station searches for a channel with a constraint of four or less.If any such channels are found, the base station determines whether theyare full 108. A channel is full if it is already in use by the basestation to communicate with the maximum number of terminals allowed bythe co-spatial constraints. In the example, if the base station finds achannel with constraint four, already in use by four terminals, thenthat channel is full. The channel is full because the addition of evenone additional terminal will result in each preexisting terminal on thechannel sharing the channel with four other terminals. Sharing with fourother terminals is beyond the constraints of the terminals in thisexample.

If one of the appropriate channels found by the base station is notfull, for example it is in use by three or fewer terminals all having aconstraint of four, then the base station can assign the new terminal tothat channel 110. To do this, the base station uses SDMA to createanother spatial channel on the conventional channel assigned to the newterminal. The base station then updates its records 112, in thisparticular example to show this channel as now being full.

However, if all of the appropriate channels are full, the base stationcan find a less efficient alternative channel that is not full 114. Ifan available alternative channel cannot be found, the connectionrequested by the new terminal will be refused 120. If, on the otherhand, there is an alternative channel that can accommodate the newterminal that channel can be used for communications with the newterminal 116. Then, the information related to this channel is updatedto show the creation of a new spatial channel for the new terminal onthe alternative conventional channel 118.

A variety of different channel allocation methods can be applied to thepresent invention. Users can be packed into as few channels as possible,so each channel is used at maximum capacity. Alternatively, the basestation may first assign all channels accessible to it, i.e., allocatedto it, to one user terminal each. This minimizes the usage of eachchannel. Then, after all channels are assigned when a new terminalarrives, a channel already in use can be shared to accommodate the newterminal.

Alternative channels may be assigned in various different ways. In oneembodiment, if there are channels not in use at the time the newterminal arrives, then the new terminal can be assigned to one of thosechannels. This assignment will characterize the future use of thechannel. According to the invention, the co-spatial constraint of thenew terminal assigned to the previously empty conventional channel willlimit the number of other terminals that can use the same channel. Thisis because the channel should now be used to service terminals with thesame co-spatial constraint as the new terminal, if possible.

In another embodiment, the base station can assign the new terminal to achannel that is neither empty nor full, but also not the most efficient.One such channel is a channel with a higher co-spatial constraint thanthe new user. If the new user shares a channel with users that have ahigher co-spatial constraint, then all the users on that channel mustoperate at the lowest co-spatial constraint level on the channel. Whilethis can theoretically limit capacity, it does allow access to usersthat might otherwise be denied. Consider, as an example, an alternativechannel that has three user terminals sharing it, each user terminalhaving a co-spatial constraint of five. This channel is not full, sinceit can accommodate two more terminals with the same co-spatialconstraint as the terminals already using it. However, it is also notthe best channel, because the new terminal has a co-spatial constraintof four. Thus, if the new terminal is assigned to this channel, then thechannel becomes full. The system has accommodated one additional userterminal, when the channel could have supported two additional userterminals. This may be less than the optimal capacity, but twoadditional users capable of supporting a constraint of five were notseeking access to the network.

The channel preferences may be selected using various priorityclassifications. For example, the conditions under which an emptychannel is preferred over a less than ideal channel can be selected tosuit the circumstances of any particular implementation. Similarly,limits can be placed on assignments to an alternative channel. It may berequired that the co-spatial constraints of terminals sharing a channelalways be the same. Alternatively, ranges may be selected. The systemcan also have either a dynamic or a static channel allocation scheme.That is, the number of terminals each channel can support can depend onthe terminals already on the channel. Alternatively, a channel can beclassified as supporting a certain number of terminals independent ofthe terminals using the channel. Other particular aspects of the networkconfiguration can be set as appropriate to the particular network andexpected user traffic.

In the examples above, the allocation scheme is dynamic. In other words,the same conventional channel sometimes supports communications with twoterminals, at other times with five, and so on. However, a staticchannel characterization scheme can be used. In one such static scheme,each channel has a predetermined maximum number of terminals that itwill support. For example, the channels allocated to the base stationcan be divided up into co-spatial classes. If channels one through tenare available to the base station, then channels one to three can bedesignated as “one-terminal” channels (co-spatial constraint one). A“one-terminal” channel can only service one user terminal at a time.Similarly, channels four to eight and seven to ten can be designatedtwo- and three-terminal channels respectively (co-spatial constraintvalues of two and three, respectively).

Referring to FIG. 2, another embodiment of the invention using a staticchannel assignment scheme is presented. In FIG. 2, the base stationdetects the arrival of a new terminal 202, the quality parameter ismeasured 203 and a spatial strategy for the new terminal is determined204. This can be done in a manner similar to that described withreference to FIG. 1.

In FIG. 2, a search is made for available channels with the sameco-spatial constraint as that determined for the new terminal 206. Forexample, if the new terminal is to have a co-spatial constraint of two,then the new terminal is assigned to one of the constraint two channels208. In the above example, one of channels four to eight will beassigned if space is available.

If all channels with the desired co-spatial constraint are full, thenthe base station may either refuse service 212, or look for a lessefficient alternate channel 210. For example, if a constraint onechannel (one of channels one to three) is available, the new terminalmay be assigned to that channel 210 and serviced 214 rather than berefused service. Because only one terminal can use that channel in anyevent, this may be considered a reasonable network configuration trade.Further considerations can be added to the static allocation method thatmay allocate channels differently in different scenarios. The processflow of FIG. 2 is a more specific example of implementing FIG. 1.

In the example of either FIG. 1 or 2, channel allocation is not limitedto the arrival of a new terminal at a base station, but can also happenduring a connection or session. For example, during communication withthe base station, a user terminal may experience a degradation orimprovement to its reception. This may allow the co-spatial constraintof that terminal to be changed. If this occurs, the terminal can beassigned or handed over to a different channel based on this changewithout interrupting the connection or session. Such in-session channelreassignment can be used to improve the capacity of the base station,and the network. The co-spatial constraints of each terminal may bereevaluated periodically to facilitate channel reassignment.Alternately, each terminal can alert the base station when a change inits co-spatial constraint may be appropriate.

Demonstrative Example

The process flow described above in connection with FIGS. 1 and 2 isfurther demonstrated by way of example to ease understanding of theinvention. The following example described with reference to FIG. 3demonstrates how certain embodiments of the invention may be carriedout. The example is simplified for ease of understanding and in ordernot to obscure the invention.

FIG. 3 shows a base station 302 of a wireless communications systemcommunicating with four user terminals using two communicationschannels. The base station 302 uses channel one (Ch1) to communicatewith user terminal 306 and user terminal 308, and channel two (Ch2) tocommunicate with user terminal 312 and user terminal 314. The basestation 302 uses an SDMA scheme and a spatial strategy to allow morethan one user terminal to share each channel.

In FIG. 3, the base station 302 assigned a “one-other” co-spatialconstraint (constraint of two) to the user terminals 306 and 308. Sincethe two user terminals 306 and 308 share Ch1, no other user terminalscommunicating with the base station 302 can use this channel. Ch 1 isfull. However, the channel may be reused elsewhere in the network by aco-channel interferer at another base station.

On the other hand, user terminals 312 and 314, for example, aredetermined to be able to be co-spatial with two other user terminalseach. That is, they have a “two-other” co-spatial constraint (constraintof three). Accordingly, one additional user terminal may use Ch2 forcommunicating with the base station 302, provided the additionalterminal can be co-spatial with at least two other terminals. In otherwords, the additional terminal should be assigned a constraint asrestrictive or less restrictive than the constraints of the otherterminals 312 and 314. For example, a constraint four is lessrestrictive than a constraint three.

If a new user terminal 320 requests channel allocation, for example as aresult of a hand-off or hand-over request, a channel must be selected inorder to accept the new user terminal 320. In one embodiment, the basestation 302 determines the user terminal 320's co-spatial constraint.This determination may be performed according to any of the methodsdescribed with reference to FIGS. 1 and 2.

The base station 302 may determine that user terminal 320 should beco-spatial with only one other user (constraint of two). As shown inFIG. 3, there is no channel that user terminal 320 can use tocommunicate with the base station 302 so service is denied. First, Ch1is full. Second, the new user terminal's co-spatial constraint of twoeliminates channel Ch2 as an option. This is because user terminal 320should not share a channel with more than one other user terminal, andCh2 is already in use by two terminals. The new user terminal 320 isthen rejected service under the circumstances of FIG. 3 if it has aconstraint of two. At another time, if one of the user terminals sharingCh 2 terminates its connection, then user terminal 320 may be servicedon Ch2. However, this does not result in optimum capacity, because theremaining terminal would be sharing Ch 2 with only one user terminal,when it is able to share with two terminals. If, on the other hand, userterminal 320 is determined to be able to share a channel with two ormore other user terminals, then Ch2 can accommodate user terminal 320under the circumstances of FIG. 3.

While in an actual base station, there would likely be more than twochannels, in this example it is assumed that Ch1 and Ch2 are the onlyavailable channels. The relatively large number of available channels inan actual wireless system mitigates these allocation concerns. With morechannels and user terminals, more ways can be found to place userterminals with similar co-spatial constraints on the same channel. Incertain embodiments, sophisticated channel-searching methods may be usedto increase system capacity even more. Also, periodic channelreassignments can be forced to ensure efficient distribution of the basestation's frequency resources by rebalancing the channel loads.

Other Spatial Strategies

Mobile radio communications systems, such as cellular voice and dataradio systems, typically have several base stations in differentlocations available for use by mobile or fixed user terminals, such ascellular telephones or wireless web devices. Each base station typicallyis assigned a set of frequencies or communications channels to use forcommunications with the user terminals. These frequencies may bedifferent from those of neighboring base stations in order to avoidinterference between neighboring base stations. This assignment schemeis a part of the frequency reuse plan of the wireless network. As aresult, the user terminals can more easily distinguish the transmissionsreceived from one base station from the signals received from another.Alternatively, all base stations may use all of the availablefrequencies at all times, along with other signal differentiationtechniques, such as spatial division. The nearness of a base stationusing the same frequency resource depends on the frequency reuse plan ofthe system.

Each base station is assigned a set of frequency resources which areorganized into conventional channels. In a typical wireless network, aconventional channel can consist of a time slot pair in a TDMA frame ona carrier frequency. A TDMA (Time Division Multiple Access) frame maycontain, for example, eight downlink transmit time slots followed byeight uplink receive time slots. Alternatively, the downlink time slotmay be on a different carrier frequency than the uplink time slot. Acarrier frequency may be a 200 kHz band around a central frequency, suchas 800 MHz or 1.9 GHz. This band represents a frequency resource used bythe base station and its user terminals for communication. Thus, a basestation transmits to a given user terminal, for example, on the secondtransmit and receive time slots on this frequency in a given frame.Furthermore, the communications channel may be organized using commontechniques, such as FDD (Frequency Division Duplex), TDD (Time DivisionDuplex), FDMA (Frequency Division Multiple Access), and CDMA (CodeDivision Multiple Access).

Other user terminals may also be using this same conventional channel.The conventional channel may be reused at a nearby base station, used bytwo or more terminals communicating with the same base station usingSDMA, or both. Those user terminals sharing one conventional channel tocommunicate with the same base station are termed co-spatial userterminals in SDMA, because the base station uses spatial strategies todistinguish these terminals. The user terminals using the sameconventional channel to communicate with other base stations as a resultof channel reuse, are termed co-channel users or co-channel interferers.

FIG. 4 can be used to show an application of the invention to otherspatial strategies including power control. In FIG. 4, for simplicityand ease of understanding, assume that the most restrictive co-spatialconstraint a user terminal can have is a “one-other” constraint in thisembodiment. In other words, some channels can serve one terminal at atime, while other channels can serve two terminals at a time.

FIG. 4 shows a base station 402 communicating with terminals 404 and 406using channels three (Ch3) and four (Ch4), respectively. The basestation may also be using other channels to communicate with numerousother terminals (not shown). In one embodiment, the base station 402 isperiodically monitoring the distance between each terminal 404 and 406and the base station 402. The distance may be inferred from signalstrength, SNR, or other signal quality parameters including thosementioned above.

If the base station 402 determines that the new terminal 412 is too farfrom the base station to share a channel with another user, then the newterminal 412 is assigned its own channel. However, if the base station402 determines that the new terminal 412 can share a channel, then thebase station 402 checks if there are other terminals communicating withthe base station 402 that can share a channel and are not currentlydoing so. In FIG. 4, terminal 406 may be such a terminal. In this case,Ch4 will be divided into two spatial channels.

When two terminals share Ch4 according to a spatial strategy, it may bedesirable for the base station 402 to a direct a null to new terminal412 associated with a signal beam aimed at terminal 406. More precisely,the base station sends signals on Ch4 that interfere in the existing RFenvironment in such a way that terminal 412 experiences mitigatedinterference due to the co-spatial user 406. However, these signals maycause undue interference to adjoining cells if they are transmittedabove a certain threshold level of power. Terminal 409 may be too farfrom the base station 402 to be co-spatial with other terminals, becausethe power level on Ch3 is too high. If this is the case, the nulls thatthe base station 402 is able to place when transmitting signals on Ch3should be used to mitigate interference to co-channel interferers.Co-channel interferers can be thought of as terminals in other cellsusing the same conventional channel. This may help implement a moreaggressive channel reuse scheme in the communications system.

Beam-forming and null-placing are sometimes described directionally, forexample, as placing a null in the direction of a user terminal. However,null-placing can involve using multiple waveforms in such a way thatthey destructively interfere at certain spatial locations due to the RFenvironment. Furthermore, nulling or null-placing may not eliminate allinterference experienced by other users. Null-placing may only reduceinterference based on information about the RF environment and the RFcharacteristics or parameters of other user terminals.

If transmissions on a channel occur at a power at a level below thethreshold, the interference caused at nearby cells may not be severe.This threshold can be set so that signals transmitted at power levelsbelow the threshold do not unduly interfere with communicationsoccurring in nearby cells on the same or interfering channels. In thiscase, a spatial strategy can be used to split the conventional channelinto two spatial channels. Referring back to FIG. 1, the base stationcan use the obtained quality metric 103 to approximate a power levelthat should be used to communicate with the new terminal. This powerlevel can become a part of the spatial strategy determined for that user104. Furthermore, this power level can become a constraint on subsequentterminals using the channel. This can create a “low-power channel”,i.e., a channel supporting terminals transmitting signals and receivingsignals transmitted at a sufficiently low level of power. A low-powerchannel supporting only one terminal can be a good choice for co-spatialsharing. A spatial strategy can be used that focuses the power of thesignals transmitted by the base station to the new terminal, andmitigates the interference caused by those signals to the old terminal.For example, when transmitting a signal to the new terminal, the basestation can form a beam in the direction of the new terminal and place anull in the direction of the old terminal using conventional beamforming and nulling technology.

If a power level above the threshold is used, then the base station canassign an unused channel to the new terminal. The spatial strategy maystill focus the power of the signals transmitted to the new terminal,and mitigate the interference caused by these high power signals tonearby cells. In other words, the base station forms a beam in thedirection of the new terminal, and places nulls to nearby terminals andbase stations reusing the same channel.

Base Station Structure

The present invention relates to wireless communication systems and maybe a fixed-access or mobile-access wireless network using spatialdivision multiple access (SDMA) technology in combination with multipleaccess systems, such as time division multiple access (TDMA), frequencydivision multiple access (FDMA) and code division multiple access(CDMA). Multiple access can be combined with frequency divisionduplexing (FDD) or time division duplexing (TDD). FIG. 5 shows anexample of a base station of a wireless communications system or networksuitable for implementing the present invention. The system or networkincludes a number of subscriber stations, also referred to as remoteterminals or user terminals, such as that shown in FIG. 5. The basestation may be connected to a wide area network (WAN) through its hostDSP 31 for providing any required data services and connections externalto the immediate wireless system. To support spatial diversity, aplurality of antennas 3 is used, for example four antennas, althoughother numbers of antennas may be selected.

A set of spatial multiplexing weights for each subscriber station areapplied to the respective modulated signals to produce spatiallymultiplexed signals to be transmitted by the bank of four antennas. Thehost DSP 31 produces and maintains spatial signatures for eachsubscriber station for each conventional channel and calculates spatialmultiplexing and demultiplexing weights using received signalmeasurements. In this manner, the signals from the current activesubscriber stations, some of which may be active on the sameconventional channel, are separated and interference and noisesuppressed. When communicating from the base station to the subscriberstations, an optimized multi-lobe antenna radiation pattern tailored tothe current active subscriber station connections and interferencesituation is created. Suitable smart antenna technologies for achievingsuch a spatially directed beam are described, for example, in U.S. Pat.No. 5,828,658, issued Oct. 27, 1998 to Ottersten et al. and U.S. Pat.No. 5,642,353, issued Jun. 24, 1997 to Roy, III et al. The channels usedmay be partitioned in any manner. In one embodiment the channels usedmay be partitioned as defined in the GSM (Global System for MobileCommunications) air interface, or any other time division air interfaceprotocol, such as Digital Cellular, PCS (Personal Communication System),PHS (Personal Handyphone System) or WLL (Wireless Local Loop).Alternatively, continuous analog or CDMA channels can be used.

The outputs of the antennas are connected to a duplexer switch 7, whichin a TDD embodiment, may be a time switch. Two possible implementationsof the duplexer switch are as a frequency duplexer in a frequencydivision duplex (FDD) system, and as a time switch in a time divisionduplex (TDD) system. When receiving, the antenna outputs are connectedvia the duplexer switch to a receiver 5, and are converted down inanalog by RF receiver (“RX”) modules 5 from the carrier frequency to anFM intermediate frequency (“IF”). This signal then is digitized(sampled) by analog to digital converters (“ADCs”) 9. Finaldown-converting to baseband is carried out digitally. Digital filterscan be used to implement the down-converting and the digital filtering,the latter using finite impulse response (FIR) filtering techniques.This is shown as block 13. The invention can be adapted to suit a widevariety of RF and IF carrier frequencies and bands.

There are, in the present example, eight down-converted outputs fromeach antenna's digital filter 13, one per receive timeslot. Theparticular number of timeslots can be varied to suit network needs.While GSM uses eight uplink and eight downlink timeslots for each TDMAframe, desirable results can also be achieved with any number of TDMAtimeslots for the uplink and downlink in each frame. For each of theeight receive timeslots, the four down-converted outputs from the fourantennas are fed to a digital signal processor (DSP) 17 (hereinafter“timeslot processor”) for further processing, including calibration,according to one aspect of this invention. Eight Motorola DSP56300Family DSPs can be used as timeslot processors, one per receivetimeslot. The timeslot processors 17 monitor the received signal powerand estimate the frequency offset and time alignment. They alsodetermine smart antenna weights for each antenna element. These are usedin the SDMA scheme to determine a signal from a particular remote userand to demodulate the determined signal.

The output of the timeslot processors 17 is demodulated burst data foreach of the eight receive timeslots. This data is sent to the host DSPprocessor 31 whose main function is to control all elements of thesystem and interface with the higher level processing, which is theprocessing which deals with what signals are required for communicationsin all the different control and service communication channels definedin the system's communication protocol. The host DSP 31 can be aMotorola DSP56300 Family DSP. In addition, timeslot processors send thedetermined receive weights for each user terminal to the host DSP 31.The host DSP 31 maintains state and timing information, receives uplinkburst data from the timeslot processors 17, and programs the timeslotprocessors 17. In addition it decrypts, descrambles, checks errorcorrecting code, and deconstructs bursts of the uplink signals, thenformats the uplink signals to be sent for higher level processing inother parts of the base station. Furthermore DSP 31 may include a memoryelement to store data, instructions, or hopping functions or sequences.Alternatively, the base station may have a separate memory element orhave access to an auxiliary memory element. With respect to the otherparts of the base station it formats service data and traffic data forfurther higher processing in the base station, receives downlinkmessages and traffic data from the other parts of the base station,processes the downlink bursts and formats and sends the downlink burststo a transmit controller/modulator, shown as 37. The host DSP alsomanages programming of other components of the base station includingthe transmit controller/modulator 37 and the RF timing controller shownas 33.

The RF timing controller 33 interfaces with the RF system, shown asblock 45 and also produces a number of timing signals that are used byboth the RF system and the modem. The RF controller 33 reads andtransmits power monitoring and control values, controls the duplexer 7and receives timing parameters and other settings for each burst fromthe host DSP 31.

The transmit controller/modulator 37, receives transmit data from thehost DSP 31. The transmit controller uses this data to produce analog IFoutputs which are sent to the RF transmitter (TX) modules 35.Specifically, the received data bits are converted into a complexmodulated signal, up-converted to an IF frequency, sampled, multipliedby transmit weights obtained from host DSP 31, and converted via digitalto analog converters (“DACs”) which are part of transmitcontroller/modulator 37 to analog transmit waveforms. The analogwaveforms are sent to the transmit modules 35. The transmit modules 35up-convert the signals to the transmission frequency and amplify thesignals. The amplified transmission signal outputs are sent to antennas3 via the duplexer/time switch 7.

User Terminal Structure

FIG. 6 depicts an example component arrangement in a remote terminalthat provides data or voice communication. The remote terminal's antenna45 is connected to a duplexer 46 to permit the antenna 45 to be used forboth transmission and reception. The antenna can be omni-directional ordirectional. For optimal performance, the antenna can be made up ofmultiple elements and employ spatial processing as discussed above forthe base station. In an alternate embodiment, separate receive andtransmit antennas are used eliminating the need for the duplexer 46. Inanother alternate embodiment, where time division duplexing is used, atransmit/receive (TR) switch can be used instead of a duplexer as iswell known in the art. The duplexer output 47 serves as input to areceiver 48. The receiver 48 produces a down-converted signal 49, whichis the input to a demodulator 51. A demodulated received sound or voicesignal 67 is input to a speaker 66.

The remote terminal has a corresponding transmit chain in which data orvoice to be transmitted is modulated in a modulator 57. The modulatedsignal to be transmitted 59, output by the modulator 57, is up-convertedand amplified by a transmitter 60, producing a transmitter output signal61. The transmitter output 61 is then input to the duplexer 46 fortransmission by the antenna 45.

The demodulated received data 52 is supplied to a remote terminalcentral processing unit 68 (CPU) as is received data before demodulation50. The remote terminal CPU 68 can be implemented with a standard DSP(digital signal processor) device such as a Motorola series 56300 FamilyDSP. This DSP can also perform the functions of the demodulator 51 andthe modulator 57. The remote terminal CPU 68 controls the receiverthrough line 63, the transmitter through line 62, the demodulatorthrough line 52 and the modulator through line 58. It also communicateswith a keyboard 53 through line 54 and a display 56 through line 55. Amicrophone 64 and speaker 66 are connected through the modulator 57 andthe demodulator 51 through lines 65 and 66, respectively for a voicecommunications remote terminal. In another embodiment, the microphoneand speaker are also in direct communication with the CPU to providevoice or data communications. Furthermore remote terminal CPU 68 mayalso include a memory element to store data, instructions, and hoppingfunctions or sequences. Alternatively, the remote terminal may have aseparate memory element or have access to an auxiliary memory element.

In one embodiment, the speaker 66, and the microphone 64 are replaced oraugmented by digital interfaces well-known in the art that allow data tobe transmitted to and from an external data processing device (forexample, a computer). In one embodiment, the remote terminal's CPU iscoupled to a standard digital interface such as a PCMCIA interface to anexternal computer and the display, keyboard, microphone and speaker area part of the external computer. The remote terminal's CPU 68communicates with these components through the digital interface and theexternal computer's controller. For data only communications, themicrophone and speaker can be deleted. For voice only communications,the keyboard and display can be deleted.

General Matters

In the description above, for the purposes of explanation, numerousspecific details are set forth in order to provide a thoroughunderstanding of the present invention. It will be apparent, however, toone skilled in the art that the present invention may be practicedwithout some of these specific details. In other instances, well-knownstructures and devices are shown in block diagram form.

The present invention includes various steps. The steps of the presentinvention may be performed by hardware components, such as those shownin FIGS. 5 and 6, or may be embodied in machine-executable instructions,which may be used to cause a general-purpose or special-purposeprocessor or logic circuits programmed with the instructions to performthe steps. Alternatively, the steps may be performed by a combination ofhardware and software. The steps have been described as being performedby either the base station or the user terminal. However, many of thesteps described as being performed by the base station may be performedby the user terminal and vice versa. Furthermore, the invention isequally applicable to systems in which terminals communicate with eachother without either one being designated as a base station, a userterminal, a remote terminal or a subscriber station. Thus, the presentinvention is equally applicable and useful in a peer-to-peer wirelessnetwork of communications devices using spatial processing. Thesedevices may be cellular phones, PDA's, laptop computers, or any otherwireless devices. Generally, since both the base stations and theterminals use radio waves, these communications devices of wirelesscommunications networks may be generally referred to as radios.

In portions of the description above, only the base station is describedas performing spatial processing using an adaptive antenna array.However, the user terminals can also contain antenna arrays, and canalso perform spatial processing both on receiving and transmitting(uplink and downlink) within the scope of the present invention.

Furthermore, in portions of the description above, certain functionsperformed by a base station could be coordinated across the network, tobe performed cooperatively with a number of base stations. For example,in certain embodiments of the present invention, a co-spatial constrainton a channel means that only a certain number of terminals may use thechannel to communicate with a base station. However, the same conceptcould be defined as a limitation on the number of terminals using thesame channel in two or more adjoining cells to communicate withdifferent base station. Thus, actions described as taken by one basestation may actually be distributed among several base stations in thesystem.

The present invention may be provided as a computer program product,which may include a machine-readable medium having stored thereoninstructions, which may be used to program a computer (or otherelectronic devices) to perform a process according to the presentinvention. The machine-readable medium may include, but is not limitedto, floppy diskettes, optical disks, CD-ROMs, and magneto-optical disks,ROMs, RAMs, EPROMs, EEPROMs, magnet or optical cards, flash memory, orother type of media/machine-readable medium suitable for storingelectronic instructions. Moreover, the present invention may also bedownloaded as a computer program product, wherein the program may betransferred from a remote computer to a requesting computer by way ofdata signals embodied in a carrier wave or other propagation medium viaa communication link (e.g., a modem or network connection).

Many of the methods are described in their most basic form, but stepscan be added to or deleted from any of the methods and information canbe added or subtracted from any of the described messages withoutdeparting from the basic scope of the present invention. It will beapparent to those skilled in the art that many further modifications andadaptations can be made. The particular embodiments are not provided tolimit the invention but to illustrate it. The scope of the presentinvention is not to be determined by the specific examples providedabove but only by the claims below.

It should also be appreciated that reference throughout thisspecification to “one embodiment” or “an embodiment” means that aparticular feature may be included in the practice of the invention.Similarly, it should be appreciated that in the foregoing description ofexemplary embodiments of the invention, various features of theinvention are sometimes grouped together in a single embodiment, figure,or description thereof for the purpose of streamlining the disclosureand aiding in the understanding of one or more of the various inventiveaspects. This method of disclosure, however, is not to be interpreted asreflecting an intention that the claimed invention requires morefeatures than are expressly recited in each claim. Rather, as thefollowing claims reflect, inventive aspects lie in less than allfeatures of a single foregoing disclosed embodiment. Thus, the claimsfollowing the Detailed Description are hereby expressly incorporatedinto this Detailed Description, with each claim standing on its own as aseparate embodiment of this invention.

1. A method comprising: assigning a co-spatial constraint to each of aplurality of conventional traffic communications channels of a basestation, the channel co-spatial constraints comprising a limitation onthe quantity of radios that can share the respective channel usingspatial division multiple access; receiving a request from a userterminal to communicate using a traffic communication channel of thebase station; measuring a quality parameter of the request received fromthe user terminal; deriving a co-spatial constraint for the userterminal based on the quality parameter, the user terminal co-spatialconstraint comprising a limitation on the quantity of additional radioswith which the user can share a conventional traffic communicationschannel using spatial division multiple access; assigning the userterminal co-spatial constraint to the user terminal; and assigning theuser terminal to one of the plurality of traffic communication channelshaving a channel co-spatial constraint that is no less than the userterminal co-spatial constraint and that has no more assigned radios thanpermitted by the channel co-spatial constraint.
 2. The method of claim1, wherein the other radios assigned to a channel have the same userterminal co-spatial constraint as the assigned user terminal.
 3. Themethod of claim 1, wherein measuring the quality parameter comprisesdetermining one or more of: a distance to the user terminal; a strengthof the received signal; a SNR of the received request, a SINR of thereceived request, a quality of service designation of the user terminal;a mobility designation of the user terminal; a mobility of the userterminal; a Doppler shift of the request; a Doppler spread of therequest; a velocity of the user terminal; and an angle spread of therequest.
 4. The method of claim 1, further comprising transmitting acommunications signal to the user terminal over the communicationschannel.
 5. The method of claim 1, further comprising transmitting nullsto the user terminal corresponding to the other radios assigned to thesame channel.
 6. The method of claim 1, further comprising: searchingfor a channel having a channel co-spatial constraint equal to the userterminal co-spatial constraint and having a number of assigned radios nomore than the channel co-spatial constraint; if a such a channel is notfound, then searching for a channel having a channel co-spatialconstraint that is less than the user terminal co-spatial constraint andhaving a number of assigned radios no more than the channel co-spatialconstraint; if such a channel is not found, then denying service to theuser terminal; and wherein assigning the user terminal comprisesassigning the user terminal to the channel found by searching.
 7. Themethod of claim 6, further comprising: reassigning other radios to otherchannels; after reassigning other radios, repeating searching for achannel having a co-spatial constraint equal to the user terminalco-spatial constraint and having no more assigned radios than permittedby the channel co-spatial constraint; and assigning the user terminal tothe found channel.
 8. The method of claim 1, further comprisingassigning a different channel co-spatial constraint to a channel havingno more assigned radios than permitted by the user terminal co-spatialconstraint and assigning the user terminal to the respective channel ifno channel is available having a channel co-spatial constraint that isno less than the user terminal co-spatial constraint and that has nomore assigned radios than permitted by the channel co-spatialconstraint.
 9. A machine-readable medium having stored thereon datarepresenting instructions, which if executed by the machine, cause themachine to perform operations comprising: assigning a co-spatialconstraint to each of a plurality of conventional traffic communicationschannels of a base station, the channel co-spatial constraintscomprising a limitation on the quantity of radios that can share therespective channel using spatial division multiple access; receiving arequest from a user terminal to communicate using a trafficcommunication channel of the base station; measuring a quality parameterof the request received from the user terminal; deriving a co-spatialconstraint for the user terminal based on the quality parameter, theuser terminal co-spatial constraint comprising a limitation on thequantity of additional radios with which the user can share aconventional traffic communications channel using spatial divisionmultiple access; assigning the user terminal co-spatial constraint tothe user terminal; and assigning the user terminal to one of theplurality of traffic communication channels having a channel co-spatialconstraint that is no less than the user terminal co-spatial constraintand that has no more assigned radios than permitted by the channelco-spatial constraint.
 10. The medium of claim 9, wherein theinstructions further cause the machine to transmit nulls to the userterminal corresponding to the other radios assigned to the same channel.11. The medium of claim 9, wherein the instructions further cause themachine to perform further operations comprising: searching for achannel having a channel co-spatial constraint equal to the userterminal co-spatial constraint and having a number of assigned radios nomore than the channel co-spatial constraint; if a such a channel is notfound, then searching for a channel having a channel co-spatialconstraint that is less than the user terminal co-spatial constraint andhaving a number of assigned radios no more than the channel co-spatialconstraint; if such a channel is not found, then denying service to theuser terminal; and wherein assigning the user terminal comprisesassigning the user terminal to the channel found by searching.
 12. Acommunications device comprising: a receiver to receive a request from auser terminal to communicate using a traffic communication channel of abase station; and a processor communicatively coupled to the receiverto: assign a co-spatial constraint to each of a plurality ofconventional traffic communications channels of the base station, thechannel co-spatial constraints comprising a limitation on the quantityof radios that can share the respective channel using spatial divisionmultiple access; measure a quality parameter of the request receivedfrom the user terminal; derive a co-spatial constraint for the userterminal based on the quality parameter, the user terminal co-spatialconstraint comprising a limitation on the quantity of additional radioswith which the user can share a conventional traffic communicationschannel using spatial division multiple access; assign the user terminalco-spatial constraint to the user terminal; and assign the user terminalto one of the plurality of traffic communication channels having achannel co-spatial constraint that is no less than the user terminalco-spatial constraint and that has no more assigned radios thanpermitted by the channel co-spatial constraint.
 13. The apparatus ofclaim 12, further comprising a transmitter to transmit a communicationssignal to the user terminal over the communications channel.
 14. Theapparatus of claim 13, wherein the transmitter further transmits nullsto the user terminal corresponding to the other radios assigned to thesame channel.
 15. A method comprising: measuring a quality parameter ofa signal received from a second radio at a first radio; deriving aco-spatial constraint for the second radio based on the qualityparameter, the co-spatial constraint comprising a limitation on thequantity of additional radios with which the second radio can share oneof a plurality of conventional communications channels using spatialdivision multiple access; assigning the co-spatial constraint to thesecond radio; assigning the second radio to one of a plurality oftraffic communication channels by first assigning the second radio to anunused channel, if available, and if not available then by secondassigning the second radio to a channel to which only one other radio isalready assigned, if available, and if not available then by thirdassigning the second radio to a channel to which only two other radiosare already assigned, if available, wherein the number of other radiosalready assigned does not exceed the co-spatial constraint; and sharingeach traffic communication channel to which more than one radio isassigned using spatial division multiple access.
 16. The method of claim15, wherein the second radio is assigned to a channel to which at leastone other radio is assigned and wherein the other assigned radios eachhave an assigned co-spatial constraint and wherein the co-spatialconstraints of the other assigned radios are greater than or equal tothat of the second radio.
 18. The method of claim 15, further comprisingassigning a co-spatial restraint to the channel to which the secondradio is assigned based on the co-spatial constraint of the secondradio.
 17. The method of claim 15, wherein determining the qualityparameter of the second radio comprises determining one or more of adistance of the second radio from the first radio, a strength of thereceived signal, a SNR of the received signal, a SINR of the receivedsignal, a quality of service designation of the second radio, a mobilitydesignation of the second radio, a mobility of the second radio, aDoppler shift of the received signal, a Doppler spread of the receivedsignal, a velocity of the second radio, and an angle spread of thereceived signal.
 19. The method of claim 15, wherein determining thequality parameter, and selecting the communications channel areperformed by the first radio, the first radio being comprised of a basestation and the second radio being comprised of one of a plurality ofsubscriber units.